Inertia switches



June 9, 1959 s. P. CLURMAN INERTIA SWITCHES Filed Nov. 9, 195a IN V EN TOR.

R M w? X Y EM N my m United States Patent INERTIA SWITCHES Stanley P. Clurman, New York, N.Y., assignor to Gordon W. Wholey, New York, NY.

Application November 9, 1956, Serial No. 621,266

2 Claims. (Cl. 200-6145) This invention relates to electric switches in general and to inertia activated switches in particular.

Inertia switches usually contain a restrained, movable mass. The inertia of this mass will move it against the restraining means relative to the switch so that the mass will act to close an electrical contact when the entire switch assembly is subjected to a sufficient acceleration or deceleration. In many applications, the inertia switch is used in connection with a relay so that contact need only be made momentarily.

An object of this invention is to provide an improved inertia switch wherein the means tending to restrain the movable mass is an adjustably positioned permanent magnet and the movable mass is of a magnetic material adapted to roll with little friction in such a manner as to increase the distance between the permanent magnet and the movable mass.

A further object of this invention is to provide an improved generally cylindrical inertia switch which may be easily adjusted to vary the response of the switch to close an electrical circuit over a range of greater or lesser accelerations imparted to the switch in directions trans verse to the axis of the switch.

A further object is to provide an improved inertia switch including fixed spaced electrodes, with a cylindrical permanent magnet adjustably positioned near the electrodes to vary the magnetic field existing between the electrodes without changing the spacing of the electrodes, and with a ball of magnetic material rollable in a recess on one electrode in the magnetic field between the electrodes, to contact both electrodes simultaneously in response to an accelerating force directed in a plane transverse to the axis of the magnet.

A still further object ofthis invention is to provide an improved inertia switch of the type described which may be made to reset itself automatically by rolling in said recess toward said magnet when the activating force of acceleration ceases.

An additional object of this invention is to provide an improved inertia switch having a cylindrical magnet adjustably positioned therein so that the switch may be made sensitive to a given acceleration in one plane transverse to the axis of the magnet, to greater or lesser accelerations in different directions in said one plane, or to a component of an acceleration in one of said directions only.

Another object of this invention is to provide an improved inertia switch which is smaller, more rugged, easier to manufacture and less costly.

Additional objects, advantages and features of invention reside in the construction, arrangement and combination of the parts involved in the embodiments of the invention as will be understood from the following description and accompanying drawings wherein Fig. 1 is a longitudinal section through one embodiment of the invention;

Fig. 2 is a section taken on line 22 in Fig. 1; and

Fig. 3 is a longitudinal section through another embodiment of the invention.

As shown in Fig. l and Fig. 2,, the device comprises an outer hollow case 10 preferably of a non-magnetic material such as brass, aluminum or plastic which has disposed within it the cylindrical insulating sleeve 11. Pressed into the upper portion of said sleeve is the circularly cylindrical hollow electrode 12 with the cylindrical hollow electrode 13 pressed into position on sleeve 11 and spaced from electrode 12. Both electrodes should be made of a non-magnetic electrically conducting material such as brass or copper. Passing through the apertures 14 and 15 in the outer case are the leads 16 and 17 which are connected to the electrodes.

Resting in the outwardly flared recess 18 in the upper surface of the retaining electrode 13 is the ball 19 of a magnetic material. The lower portion of the outer case is closed with the plug member 20 which may be screwed axially by means of the slot 21. Rigidly fixed to said plug member is the permanent magnet 22.

As shown in Fig. 3, another embodiment of the device comprises an upper cup-shaped case member 26 of a non-magnetic, electrically conducting material seated upon the plastic annular insulator 23. Extending upwards within said insulator so as not to touch the upper case is the upper cylindrical extension 25 of the lower case member 24. Resting in the outwardly flared recess 18 in the upper surface of the upper wall of extension 25 is the ball 19 of magnetic material. The lower im ternally threaded cylindrical bore of the lower case mernber 24 is closed with the threaded plug 20 which may be screwed axially into place by means of the slot 21. Rigidly fixed in the plug is the cylindrical permanent magnet 22 which extends axially into extension 25 and which is adjustably spaceable from the end wall of the extension by turning the plug in the bore.

The switch operates in the following manner. In both embodiments of the invention, the ball 19 is drawn to the lowest portion of the recess 18 bythe permanent magnet 22. If the switch is accelerated to the right for example, in a direction transverse to the axis of the magnet, the inertia of the ball tends to cause it to roll upwardly in the recess 18 to the left. To do this, the acceleration has to be sufficient to cause the ball to roll upwards out of the recess against the attraction of the magnet in the magnetic field existing beyond the end wall of the extension If the force of this acceleration is great enough and of sufiicient duration, the ball in Fig. 1 would be arrested by the circular electrode 12. At this moment the ball would close an electrical circuit so that a current could fiow from lead 15 through the circular electrode through the ball through the retaining electrode to lead 16. In a like manner, the ball in Fig. 3 would be arrested by the upper case. At this moment, the ball would close an electrical circuit so that a current could flow from the upper case 26 through the ball to the lower case element 24. The embodiment in Fig. 3 needs no leads as it would be mounted in a mounting similar to a standard fuse holder so that the upper case and the lower case element would make separate electrical contacts with the holder.

The current flowing through the switch, though it may have a duration of only a few milli-seconds, is suflicient to activate a relay which in turn can activate any desired apparatus. When the acceleration ceases, the magnet will act to decrease the distance between itself and the ball which will then roll to the lowest portion of the recess so that the switch is ready to be activated again by another acceleration.

It is to be noted that this inertia switch is only sensitive to an acceleration transverse to the axis of the magnet generally normal to the position of the magnet and the ball. That a violent acceleration upwards or downwards axially in the cylindrical case will not activate the switch is a. desirable characteristic it the switch is used in aircraft and the like to activate emergency equipment in the case of a crash. In this sort of an application, a rough landing will not activate a switch placed in a vertical position. Only a crash with the attendant deceleration in a horizontal plane will operate it.

To adjust the switch to be sensitive to a specific force of acceleration in a transverse direction to the aligned axes of the case and magnet, the plug member 28 may be calibrated in relation to the outer case or the lower case element and screwed upwards or downwards axial ly to increase or decrease the distance between the magnet and the ball. The closer the magnet to the ball, the greater the acceleration required to activate the switch. Also, the smaller the ring electrode or the upper case is made in relation to the ball, the shorter the duration of the acceleration need be to activate the switch.

it has been found in the practice of this invention that a ball one cuarter of an inch in diameter resting in a conical. recess the sides of which are inclined ten degrees to the horizontal and used in conjunction with a cylindrical alnico magnet one quarter of an inch in diameter and one inch long gives the best results when reacting to accelerations between one and five gravities. If a larger ball and magnet are used, the ball tends to be too massive for the retaining force as the ball exceeds one half an inch in diameter.

If the switch is to be sensitive to different degrees in different directions, the recess need not be conical. It could slope gently in the directions the switch is to be sensitive and more steeply in the directions the switch is to be less sensitive. Also in place of a recess, the ball could be placed in a hole of such a diameter that the edges of the hole would contact the ball in such a way that the tangents to the points of contact would be inclined to the horizontal to the same extent as the sides of the recess.

If it is considered desirable, the recess may be sur rounded by a lower, downward sloping portion so that the ball will not roll back into the recess when the acceleration ceases but will maintain an electrical contact between the two electrodes as it is held against them by the magnet. The permanent magnet may be replaced by an equivalent electromagnet if this is considered desirable for a specific application. In addition, the upper electrode need not be circular if it is desired to have the switch sensitive to different durations of acceleration in different directions. could be oval or tear shaped in which case it would take the ball longer to roll to the more distant portion of the electrode. This invention is not limited to the use of a ball as the rolling element of mass. A cylinder in a trough shaped recess could be used to make the switch sensitive to accelerations in one or two directions only.

I have here shown and described several preferred embodiments of my invention. It will be apparent, however, that this invention is not limited to these embodirnents, and that many changes, additions and modifications can be made in connection therewith without departing from the spirit and scope of the invention as herein disclosed and hereinafter claimed.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. An inertia switch, comprising a cylindrical case member formed of non-magnetic electrically conductive material and having an internally threaded bore, a

For example, the upper electrode r threaded plug axially positionable in said bore, a cylindrical permanent bar magnet mounted in said plug and movable axially thereby in said bore, said member having a cylindrical hollow extension with an external diameter smaller than the external diameter of said member to provide an annular end portion on said member, said extension terminating in a free end wall, said wall having an external outwardly flared recess formed therein, an annular electrical insulator seated on said annular end portion of said member, a cup-shaped case member formed of non-magnetic electrically conductive material having an open end seated on said insulator in axial alignment with the first named case member, said extension projecting into said cup-shaped member and being radially spaced therefrom, said magnet extending into said extension and having a free end adjustably spaceable from said end wall by rotation of said plug in said bore to provide a magnetic field of variable intensity beyond said wall within said cup-shaped case member, and a spherical ball of magnetic material retained in said recess by said magnetic field, said ball being displaceable from said recess by rolling therein toward the free end of said extension to contact cup-shaped member and said extension simultaneously in response to a force of predetcrmined magnitude applied transversely to the axis of said magnet, the intensity of said field being sufiicient to prevent outward movement of the ball in the direction of the axis of the magnet upon application of said force, the magnitude of the force required to displace said ball being determined by the variable space between the free end of the magnet and the end wall of said extension.

2. An inertia switch, comprising a case member formed of non-magnetic electrically conductive material and having an internally threaded cylindrical bore, a threaded plug axially positionable in said bore, a cylindrical permanent bar magnet mounted in said plug and movable axially thereby in said bore, said member carrying a cylindrical hollow element terminating in a free end wall, said wall having an external outwardly flared recess formed therein, an electrical insulator seated around said element, another case member formed of non-magnetic electrically conductive material having a hollow body seated on said insulator, said element being spaced a fixed distance from said body, said magnet extending into said element and having a free end adjustably spaceable from said end wall by rotation of said plug in said bore to provide a magnetic field of variable intensity beyond said wall within said body without changing the fixed spacing between said wall and said body, and a spherical ball of magnetic material retained in said recess by said magnetic field, said ball being displaceable from said recess by rolling therein toward the free end of said element to contact said body and said element simultaneously in response to a force of predetermined magnitude applied transversely to the axis of said magnet, the magnitude of the force required to displace said ball being determined by the variable space between the free end of the magnet and the end wall of said element.

References Cited in the file of this patent UNITED STATES PATENTS 1,662,979 Nelson Mar. 20, 1928 2,415,086 Detwiler Feb. 4, 1947 2,744,976 Black May 8, 1956 2,791,653 Haberland c- May 7, 1957 

